Centrifugal compresser with seal bearing

ABSTRACT

A centrifugal compressor to be used in a chiller system includes a casing, an impeller, a motor and a diffuser. The casing has an inlet portion and an outlet portion. The impeller is attached to a shaft rotatable about a rotation axis, and has an impeller shroud which encloses the impeller. The motor rotates the shaft in order to rotate the impeller. The diffuser is disposed in the outlet portion downstream of the impeller. The centrifugal compressor further includes a seal bearing. The seal bearing is attached to the inlet portion to seal the impeller shroud, and rotatably supports the impeller and the shaft.

BACKGROUND Field of the Invention

The present invention generally relates to a centrifugal compressor usedin a chiller system. More specifically, the present invention relates toa centrifugal compressor with a seal bearing.

Background Information

A chiller system is a refrigerating machine or apparatus that removesheat from a medium. Commonly a liquid such as water is used as themedium and the chiller system operates in a vapor-compressionrefrigeration cycle. This liquid can then be circulated through a heatexchanger to cool air or equipment as required. As a necessarybyproduct, refrigeration creates waste heat that must be exhausted toambient or, for greater efficiency, recovered for heating purposes. Aconventional chiller system often utilizes a centrifugal compressor,which is often referred to as a turbo compressor. Thus, such chillersystems can be referred to as turbo chillers. Alternatively, other typesof compressors, e.g. a screw compressor, can be utilized.

In a conventional (turbo) chiller, refrigerant is compressed in thecentrifugal compressor and sent to a heat exchanger in which heatexchange occurs between the refrigerant and a heat exchange medium(liquid). This heat exchanger is referred to as a condenser because therefrigerant condenses in this heat exchanger. As a result, heat istransferred to the medium (liquid) so that the medium is heated.Refrigerant exiting the condenser is expanded by an expansion valve andsent to another heat exchanger in which heat exchange occurs between therefrigerant and a heat exchange medium (liquid). This heat exchanger isreferred to as an evaporator because refrigerant is heated (evaporated)in this heat exchanger. As a result, heat is transferred from the medium(liquid) to the refrigerant, and the liquid is chilled. The refrigerantfrom the evaporator is then returned to the centrifugal compressor andthe cycle is repeated. The liquid utilized is often water.

A conventional centrifugal compressor basically includes a casing, aninlet guide vane, an impeller, a diffuser, a motor, various sensors anda controller. Refrigerant flows in order through the inlet guide vane,the impeller and the diffuser. Thus, the inlet guide vane is coupled toa gas intake port of the centrifugal compressor while the diffuser iscoupled to a gas outlet port of the impeller. The inlet guide vanecontrols the flow rate of refrigerant gas into the impeller. Theimpeller increases the velocity of refrigerant gas. The diffuser worksto transform the velocity of refrigerant gas (dynamic pressure), givenby the impeller, into (static) pressure. The motor rotates the impeller.The controller controls the motor, the inlet guide vane and theexpansion valve. In this manner, the refrigerant is compressed in aconventional centrifugal compressor. A conventional centrifugalcompressor may have one or two stages. A motor rotates one or moreimpellers via shaft. A bearing system supports the shaft of the motor.The impeller of a conventional centrifugal compressor includes a closedimpeller, a semi-open impeller or an open impeller. A closed impeller ora semi-open impeller has an impeller shroud which encloses the impeller.

U.S. Patent Application Publication No. 2015/0192147 has disclosed acentrifugal compressor which uses a closed impeller.

SUMMARY

In a conventional centrifugal compressor which uses a closed impeller,bearings and a seal for the impeller shroud are necessary components. Ina conventional centrifugal compressor, however, a bearing system and aseal for the impeller shroud are provided separately. It has beenconsidered difficult to fit a bearing in the inlet portion of thecompressor because the inlet portion of the compressor needs to be of asignificantly large size to accommodate a bearing. In a conventionalcentrifugal compressor, therefore, a bearing system is providedtypically only around the shaft of the motor.

Therefore, one object of the present invention is to provide acentrifugal compressor which has an integral seal bearing to provide aseal and a bearing in the compressor to improve the efficiency and therotordynamic performance of the compressor.

Another object of the present invention is to provide a centrifugalcompressor which has an integral seal bearing to provide a seal and abearing in the compressor relatively simple with reduced costs.

One or more of the above objects can basically be attained by providinga centrifugal compressor adapted to be used in a chiller system, thecentrifugal compressor including a casing having an inlet portion and anoutlet portion, an impeller attached to a shaft rotatable about a shaftrotation axis, the impeller having an impeller shroud which encloses theimpeller, a motor configured and arranged to rotate the shaft in orderto rotate the impeller, a diffuser disposed in the outlet portiondownstream of the impeller, and a seal bearing attached to the inletportion to seal the impeller shroud, and rotatably supporting theimpeller and the shaft.

These and other objects, features, aspects and advantages of the presentinvention will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theannexed drawings, discloses preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a schematic diagram illustrating a chiller system whichincludes a centrifugal compressor with seal bearings in accordance withan embodiment of the present invention;

FIG. 2 is a perspective view of the centrifugal compressor of thechiller system illustrated in FIG. 1, with portions broken away andshown in cross-section for the purpose of illustration;

FIG. 3 is a schematic longitudinal side view of the impellers and motorof the centrifugal compressor illustrated in FIG. 2;

FIG. 4 is an enlarged perspective view of the seal bearing mounted on animpeller shroud of the impeller illustrated in FIG. 2, with portionsbroken away and shown in cross-section for the purpose of illustration;

FIG. 5 is a perspective view of part of the seal bearing;

FIG. 6A is a front view of one of the impellers illustrated in FIG. 2,as seen from the inlet side of the centrifugal compressor and FIG. 6B isa perspective view thereof;

FIG. 7 is a simplified cross-sectional view of the seal bearing and theimpeller shroud of the impeller illustrated in FIGS. 2-4, 6A and 6B, astaken along section line 7-7 in FIG. 6A;

FIG. 8 is an enlarged schematic cross-sectional view of the seal bearingand the impeller shroud of the impeller inside circle 8 in FIG. 7;

FIG. 9A is a schematic diagram illustrating a back-to-back impellerconfiguration and FIG. 9B is a schematic diagram illustrating an inlineimpeller configuration;

FIG. 10 illustrates an oil refrigerant separation system which includesan oil sump, an oil supply line, an oil return line, a refrigerant line,and a separation line; and

FIG. 11 is a schematic diagram of the chiller controller of the chillersystem of FIG. 1.

DETAILED DESCRIPTION OF EMBODIMENT(S)

Selected embodiments will now be explained with reference to thedrawings. It will be apparent to those skilled in the art from thisdisclosure that the following descriptions of the embodiments areprovided for illustration only and not for the purpose of limiting theinvention as defined by the appended claims and their equivalents.

Referring initially to FIG. 1, a chiller system 10, which includes aseal bearing 60 (60 a, 60 b), is illustrated in accordance with anembodiment of the present invention. The chiller system 10 is preferablya water chiller that utilizes cooling water and chiller water in aconventional manner. The chiller system 10 illustrated herein is atwo-stage chiller system. However, it will be apparent to those skilledin the art from this disclosure that the chiller system 10 could be asingle stage chiller system or a multiple stage chiller system includingthree or more stages.

The chiller system 10 basically includes a chiller controller 20, acompressor 22, a condenser 24, an expansion valve 26, and an evaporator28 connected together in series to form a loop refrigeration cycle. Inaddition, various sensors (not shown) are disposed throughout thecircuit of the chiller system 10. The chiller system 10 is conventionalexcept that the chiller system has the seal bearing 60 (60 a, 60 b) inaccordance with the present invention.

Referring to FIGS. 1-3, the compressor 22 is a two-stage centrifugalcompressor in the illustrated embodiment. The compressor 22 illustratedherein is a two-stage centrifugal compressor which includes twoimpellers. However, the compressor 22 can be a multiple stagecentrifugal compressor including three or more impellers. The two-stagecentrifugal compressor 22 of the illustrated embodiment includes a firststage impeller 34 a and a second stage impeller 34 b. The impeller 34 ahas an impeller shroud 35 a which encloses the impeller 34 a, and theimpeller 34 b has an impeller shroud 35 b which encloses the impeller 34b. The centrifugal compressor 22 further includes a first stage inletguide vane 32 a, a first diffuser/volute 36 a, a second stage inletguide vane 32 b, a second diffuser/volute 36 b, and a compressor motor38 as well as various conventional sensors (not shown). A casing 30covers the centrifugal compressor 22. The casing 30 includes an inletportion 31 a and an outlet portion 33 a for the first stage of thecompressor 22. The casing 30 also includes an inlet portion 31 b and anoutlet portion 33 b for the second stage of the compressor 22.

The chiller controller 20 receives signals from the various sensors andcontrols the inlet guide vanes 32 a and 32 b, and the compressor motor38 in a conventional manner, as explained in more detail below.Refrigerant flows in order through the first stage inlet guide vane 32a, the first stage impeller 34 a, the second stage inlet guide vane 32b, and the second stage impeller 34 b. The inlet guide vanes 32 a and 32b control the flow rate of refrigerant gas into the impellers 34 a and34 b, respectively, in a conventional manner. The impellers 34 a and 34b increase the velocity of refrigerant gas, generally without changingpressure. The motor speed determines the amount of increase of thevelocity of refrigerant gas. The diffusers/volutes 36 a and 36 bincrease the refrigerant pressure. The diffusers/volutes 36 a and 36 bare non-movably fixed relative to the casing 30. The compressor motor 38rotates the impellers 34 a and 34 b via a shaft 42. In this manner, therefrigerant is compressed in the centrifugal compressor 22. Thecentrifugal compressor 22 of the illustrated embodiment includes theinlet guide vanes 32 a and 32 b. However, the inlet guide vanes 32 a and32 b are optional, and the seal bearing 60 (60 a, 60 b) in accordancewith the present invention can be applied to a centrifugal compressorwhich does not include an inlet guide vane.

In operation of the chiller system 10, the first stage impeller 34 a andthe second stage impeller 34 b of the compressor 22 are rotated, and therefrigerant of low pressure in the chiller system 10 is sucked by thefirst stage impeller 34 a. The flow rate of the refrigerant is adjustedby the inlet guide vane 32 a. The refrigerant sucked by the first stageimpeller 34 a is compressed to intermediate pressure, the refrigerantpressure is increased by the first diffuser/volute 36 a, and therefrigerant is then introduced to the second stage impeller 34 b. Theflow rate of the refrigerant is adjusted by the inlet guide vane 32 b.The second stage impeller 34 b compresses the refrigerant ofintermediate pressure to high pressure, and the refrigerant pressure isincreased by the second diffuser/volute 36 b. The high pressure gasrefrigerant is then discharged to the chiller system 10.

Referring to FIGS. 1 and 11, the chiller controller 20 is an electroniccontroller that includes a compressor variable frequency drive 92, acompressor motor control section 93, an inlet guide vane control section94, an expansion valve control section 95, and an oil refrigerantseparation system control section 96.

In the illustrated embodiment, the control sections are sections of thechiller controller 20 programmed to execute the control of the partsdescribed herein. The compressor variable frequency drive 92, thecompressor motor control section 93, and the inlet guide vane controlsection 94, the expansion valve control section 95, and the oilrefrigerant separation system control section 96 are coupled to eachother, and form parts of a centrifugal compressor control portion thatis electrically coupled to an I/O interface of the compressor 22.However, it will be apparent to those skilled in the art from thisdisclosure that the precise number, location and/or structure of thecontrol sections, portions and/or chiller controller 20 can be changedwithout departing from the present invention so long as the one or morecontrollers are programmed to execute control of the parts of thechiller system 10 as explained herein.

The chiller controller 20 is conventional, and thus, includes at leastone microprocessor or CPU, an Input/output (I/O) interface, RandomAccess Memory (RAM), Read Only Memory (ROM), a storage device (eithertemporary or permanent) forming a computer readable medium programmed toexecute one or more control programs to control the chiller system 10.The chiller controller 20 may optionally include an input interface suchas a keypad to receive inputs from a user and a display device used todisplay various parameters to a user. The parts and programming areconventional, and thus, will not be discussed in detail herein, exceptas needed to understand the embodiment(s).

As mentioned above, the chiller system 10 has the seal bearing 60 (60 a,60 b) in accordance with the present invention. In the illustratedembodiment, the compressor 22 is a two-stage centrifugal compressor. Afirst stage seal bearing 60 a and a second stage seal bearing 60 b areprovided in the first stage and the second stage of the compressor 22,respectively, as shown in FIG. 1. It will be apparent to those skilledin the art from this disclosure that the structures of the first stageseal bearing 60 a and the second stage seal bearing 60 b are identical,except that they are mirror images of each other. Therefore, the firststage seal bearing 60 a and the second stage seal bearing 60 b arecollectively referred to as the seal bearing 60 hereinafter.

In the same manner, the elements of the first stage and the second stageof the compressor 22 are collectively referred to hereinafter withoutbeing distinguished. For example, the inlet portion 31 a of the casing30 for the first stage and the inlet portion 31 b of the casing 30 forthe second stage are collectively referred to as the inlet portion 31 ofthe casing 30. The first stage inlet guide vane 32 a and the secondstage inlet guide vane 32 a are collectively referred to as the inletguide vane 32. The first stage impeller 34 a and the second stageimpeller 34 b are collectively referred to as the impeller 34.

Referring to FIGS. 4-7, the detailed structure of the seal bearing 60 inaccordance with the present invention will be explained. The sealbearing 60 is attached to the inlet portion 31 to seal the impellershroud 35 of the impeller 34, and rotatably supports the impeller 34 andthe shaft 42, as explained in more detail below. The impeller shroud 35is typically made of steel or aluminum. The seal bearing 60 can be madeof/lined with steel. However, it will be apparent to those skilled inthe art from this disclosure that another material can be used withoutdeparting from the present invention. As best shown in FIGS. 6A and 6B,a closed impeller is used as the impeller 34 of the compressor 22 in theillustrated embodiment. However, the present invention is not limited tothe type of the impeller 34. The seal bearing 60 in accordance with thepresent invention can also be applied to another type of impeller solong as it has a shroud. The seal bearing 60 may be a radial bearing ora thrust bearing

As best shown in FIG. 8, the seal bearing 60 includes an oil supplygroove 62, an upstream oil return groove 64, a downstream oil returngroove 66, an upstream separation groove 68, and a downstream separationgroove 70 in the illustrated embodiment. The oil supply groove 62 isprovided between an upstream center projection 63 and a downstreamcenter projection 65 of the seal bearing 60. The upstream separationgroove 68 is provided between an upstream end projection 67 and anupstream intermediate projection 69 of the seal bearing 60. The upstreamoil return groove 64 is provided between the upstream center projection63 and the upstream intermediate projection 69 of the seal bearing 60.The downstream separation groove 70 is provided between a downstreamintermediate projection 71 and a downstream end projection 73 of theseal bearing 60. The downstream oil return groove 66 is provided betweenthe downstream center projection 65 and the downstream intermediateprojection 71 of the seal bearing 60. The oil supply groove 62, theupstream oil return groove 64, the downstream oil return groove 66, theupstream separation groove 68, and the downstream separation groove 70are formed on a shroud facing surface 61 of the seal bearing 60 whichfaces the impeller shroud 35.

In the illustrated embodiment, the width of the oil supply groove 62along an axial direction parallel to the rotational axis X is largerthan the widths of the upstream oil return groove 64, the downstream oilreturn groove 66, the upstream separation groove 68, and the downstreamseparation groove 70. However, it will be apparent to those skilled inthe art from this disclosure that the width of the oil supply groove 62may be substantially the same as the widths of the upstream oil returngroove 64, the downstream oil return groove 66, the upstream separationgroove 68, and the downstream separation groove 70 without departingfrom the scope of the present invention.

As shown in FIGS. 4 and 8, the impeller shroud 35 has a stepped part35S. The stepped part 35S outwardly projects in a direction Yperpendicular to the rotational axis X. The seal bearing 60 has arecessed part 60R. The recessed part 60R receives the stepped part 35S.A gap 72 exists between the stepped part 35S of the impeller shroud 35and the recessed part 60R of the seal bearing 60. The oil supply groove62 is provided in the recessed part 60R. Thus, the height of the oilsupply groove 62 along a direction Y perpendicular to the axialdirection is smaller than the heights of the upstream oil return groove64, the downstream oil return groove 66, the upstream separation groove68, and the downstream separation groove 70. The recess/step combinationis used to minimize leakage of oil from the return groove to theseparation groove through centrifugal action. However, the recess/stepcombination is optional. It will be apparent to those skilled in the artfrom this disclosure that the recess/step combination can be omittedwithout departing from the present invention.

The upstream oil return groove 64 is disposed upstream of a refrigerantflow F relative to the oil supply groove 62. The downstream oil returngroove 66 is disposed downstream of the refrigerant flow F relative tothe oil supply groove 62. The refrigerant flow F is shown by arrow F inFIG. 8, which flows from the suction side of the compressor 22 to thedischarge side of the compressor 22. With this arrangement, the oilsupply groove 62 is interposed between the upstream oil return groove 64and the downstream oil return groove 66. Oil supplied to the oil supplygroove 62 flows to the upstream oil return groove 64 and the downstreamoil return groove 66 through the gap 72, as explained in more detailbelow.

The upstream separation groove 68 is disposed upstream of therefrigerant flow F relative to the upstream oil return groove 64 and theoil supply groove 62 such that the upstream oil return groove 64 isinterposed between the oil supply groove 62 and the upstream separationgroove 68. The downstream separation groove 70 is disposed downstream ofthe refrigerant flow F relative to the downstream oil return groove 66and the oil supply groove 62 such that the downstream oil return groove66 is interposed between the oil supply groove 62 and the downstreamseparation groove 70. Oil leaking from the upstream oil return groove 64and the downstream oil return groove 66 flows into the upstreamseparation groove 68 and the downstream separation groove 70,respectively. A small amount of refrigerant also flows into the upstreamseparation groove 68 and the downstream separation groove 70, asexplained in more detail below.

In the illustrated embodiment, the upstream oil return groove 64, thedownstream oil return groove 66, the upstream separation groove 68, andthe downstream separation groove 70 have substantially the same width.However, it will be apparent to those skilled in the art from thisdisclosure that different widths may be used for the upstream oil returngroove 64, the downstream oil return groove 66, the upstream separationgroove 68, and the downstream separation groove 70 without departingfrom the scope of the present invention.

Also, in the illustrated embodiment, the seal bearing 60 includes theoil supply groove 62, the upstream oil return groove 64, the downstreamoil return groove 66, the upstream separation groove 68, and thedownstream separation groove 70. However, the seal bearing 60 may haveonly the oil supply groove 62, the upstream oil return groove 64, andthe upstream separation groove 68. Similarly, the seal bearing 60 mayhave only the oil supply groove 62, the downstream oil return groove 66,and the downstream separation groove 70.

As best shown in FIG. 8, teeth 74-80 are formed on the shroud facingsurface 61 of the seal bearing 60. More specifically, the teeth 74 isformed on the shroud facing surface 61 of the upstream end projection67, the teeth 76 is formed on the shroud facing surface 61 of theupstream intermediate projection 69, the teeth 78 is formed on theshroud facing surface 61 of the downstream end projection 73, and theteeth 80 is formed on the shroud facing surface 61 of the downstreamintermediate projection 71.

The teeth 74 are located between an end of the seal bearing 60 on thesuction side of the compressor 22 with the upstream separation groove68. The teeth 76 are located between the upstream separation groove 68with the upstream oil return groove 64. The teeth 78 are located betweenan end of the seal bearing 60 on the discharge side of the compressor 22with the downstream separation groove 70. The teeth 80 are locatedbetween the downstream separation groove 70 with the downstream oilreturn groove 66. The upstream separation groove 68 receives oil andrefrigerant which pass through the teeth 74 and the teeth 76. Similarly,the downstream separation groove 70 receives oil and refrigerant whichpass through the teeth 78 and the teeth 80.

Although a small clearance exists between the tips of the teeth 74-78and the impeller shroud 35, the oil supplied to the oil supply groove 62has to pass through a long and difficult path created by the teeth 74-78to escape, and thus the teeth 74-78 serve to prevent the leakage of theoil to outside the seal bearing 60. Moreover, the oil flowing into theupstream separation groove 68 and the downstream separation groove 70 issucked into an oil sump explained below. In this manner, the leakage ofthe oil lubricating the seal bearing 60 is reduced to substantiallyzero. The seal bearing 60 serves as a seal as well as a bearing.

The upstream separation groove 68 and the downstream separation groove70 have an annular shape extending fully circumferentially around theimpeller shroud 35. The upstream oil return groove 64 and the downstreamoil return groove 66 preferably have an annular shape extending fullycircumferentially around the impeller shroud 35 in the same manner asthe upstream separation groove 68 and the downstream separation groove70. Alternatively, the upstream oil return groove 64 and the downstreamoil return groove 66 may have a shape extending partly circumferentiallyaround the impeller shroud 35. The oil supply groove 62 have an arcshape but does not need to extend fully circumferentially around theimpeller shroud 35.

FIG. 9A is a schematic diagram illustrating a back-to-back impellerconfiguration and FIG. 9B is a schematic diagram illustrating an inlineimpeller configuration. In the back-to-back impeller configuration asshown in FIG. 9A, the seal bearings 60 are used on both impeller shroudsin a simply-supported bearing configuration. However, the presentinvention is not limited to the back-to-back impeller configuration. Theseal bearing 60 in accordance with the present invention can also beapplied to the inline impeller configuration as shown in FIG. 9B. In theinline impeller configuration as shown in FIG. 9B, a conventionalbearing is used (preferably oil-lubricated) with a seal bearing 60 onone of the impellers. The oil refrigerant separation system 100 shown inFIG. 10 uses the inline impeller configuration as one example.

Referring to FIG. 1, the chiller system 10 has an oil refrigerantseparation system 100 a and an oil refrigerant separation system 100 b.It will be apparent to those skilled in the art from this disclosurethat the structures of the oil refrigerant separation system 100 a andthe oil refrigerant separation system 100 b are identical. Therefore,the oil refrigerant separation system 100 a and the oil refrigerantseparation system 100 b are collectively referred to as the oilrefrigerant separation system 100 hereinafter. Alternatively, thechiller system 10 may have a single oil refrigerant separation system100 used for both the seal bearing 60 a and the seal bearing 60 b. Thesingle oil refrigerant separation system 100 can also be applied to theinline impeller configuration as explained in more detail below.

Referring to FIG. 10, the oil refrigerant separation system 100 includesan oil sump 101, an oil supply line OSL, an oil return line ORL, arefrigerant line RL, and a separation line SL. The oil sump 101 isconfigured and arranged to receive oil and refrigerant. The oil supplyline OSL extends from the oil sump 101 to the oil supply groove 62. Anoil pump OP and an oil filter are disposed in the oil supply line OSL.The oil return line ORL extends from the upstream oil return groove 64and the downstream oil return groove 66 to the oil sump 101. A strainerand an oil cooler are disposed in the oil return line ORL. Therefrigerant line RL extends from the oil sump 101 to the suction side ofthe compressor 22. A vacuum pump VP is disposed in the refrigerant lineRL. The separation line SL extends from the upstream separation groove68 and the downstream separation groove 70 to the oil sump 101.

In the oil refrigerant separation system 100, oil lubricating the sealbearing 60 is supplied to the oil supply groove 62 from the oil sump 101via the oil supply line OSL. The oil supplied to the oil supply groove62 passes through the gap 72 and then flows to the upstream oil returngroove 64 and the downstream oil return groove 66. The oil flowing tothe upstream oil return groove 64 and the downstream oil return groove66 is returned to the oil sump 101 via the oil return line ORL. In thismanner, oil supplied to the oil supply groove 62 from the oil sump 101is mainly returned to the oil sump 101 via the upstream oil returngroove 64 and the downstream oil return groove 66.

However, some of the oil leaks from the upstream oil return groove 64and the downstream oil return groove 66 through the teeth 76 and teeth80, respectively, and flows into the upstream separation groove 68 andthe downstream separation groove 70, respectively. A small amount ofrefrigerant also flows into the upstream separation groove 68 and thedownstream separation groove 70 from the suction side of the compressor22 and the discharge side of the compressor 22, respectively. The oilcontaining the refrigerant in the upstream separation groove 68 and thedownstream separation groove 70 is sucked via vacuum created by thevacuum pump VP and introduced into the oil sump 101 via the separationline SL. In the oil sump 101, the oil containing the refrigerant isseparated into an oil portion and a refrigerant portion. The refrigerantportion is returned to the suction side of the compressor 22 by usingthe vacuum pump VP in the refrigerant line RL. The oil portion issupplied to the oil supply groove 62 by using the oil pump OP in the oilsupply line OSL. The inline impeller configuration shown in FIG. 10includes an oil bearing 40. Some of the oil in the oil sump 101 issupplied to the oil bearing 40 via the oil supply line OSL and returnedto the oil sump 101 via the oil return line ORL.

In order to achieve the above-described separation/circulation of oiland refrigerant, control is performed to satisfy the followingconditions. The control may be active control by the oil refrigerantseparation system control section 96. Alternatively, the control may bepassive control.

-   -   1. The pressure in the upstream separation groove 68 and the        downstream separation groove 70 (P₅) must be less than the        compressor suction pressure (P₇).    -   2. The pressure in the upstream oil return groove 64 and the        downstream oil return groove 66 (P₄) must be greater than the        pressure in the upstream separation groove 68 and the downstream        separation groove 70 (P₅).    -   3. The pressure in the oil supply groove 62 (P₃) must be greater        than the pressure in the upstream oil return groove 64 and the        downstream oil return groove 66 (P₄).

P₅<P₇  Condition 1:

P₅<P₄<P₃  Conditions 2 and 3:

-   -   Condition 1 is achieved by the vacuum pump VP that generates a        lower pressure in the oil sump 101 than the suction side of the        compressor 22 by creating a flow of refrigerant from the oil        sump 101 to the suction side of the compressor 22. Condition 2        is achieved by increasing a pressure drop in the oil return line        ORL compared to the separation line SL. The increased pressure        drop is caused by the components in the oil return line ORL        including the strainer, the oil cooler, an optional filter (not        shown) and an optional valve (not shown). Condition 3 is        achieved by the oil pump OP. It will be apparent to those        skilled in the art from this disclosure that the detailed sizing        of the flow generating components and piping can be determined        based on standard engineering practice.

An example of the system startup/shutdown procedure is shown in thefollowing table 1:

TABLE 1 Startup Shutdown 1. Start vacuum pump VP 1. Verify compressor inoff state 2. Start oil pump OP 2. Set compressor start to disable state3. Compressor start enable 3. Shut down oil pump OP 4. Shut down vacuumpump VP

In terms of global environment protection, use of new low GWP (GlobalWarming Potential) refrigerants such like R1233zd, R1234ze areconsidered for chiller systems. One example of the low global warmingpotential refrigerant is low pressure refrigerant in which theevaporation pressure is equal to or less than the atmospheric pressure.For example, low pressure refrigerant R1233zd is a candidate forcentrifugal chiller applications because it is non-flammable, non-toxic,low cost, and has a high COP compared to other candidates such likeR1234ze, which are current major refrigerant R134a alternatives. Thecompressor 22 having the seal bearing 60 in accordance with the presentinvention is useful with any type of refrigerant including low pressurerefrigerant such as R1233zd.

General Interpretation of Terms

In understanding the scope of the present invention, the term“comprising” and its derivatives, as used herein, are intended to beopen ended terms that specify the presence of the stated features,elements, components, groups, integers, and/or steps, but do not excludethe presence of other unstated features, elements, components, groups,integers and/or steps. The foregoing also applies to words havingsimilar meanings such as the terms, “including”, “having” and theirderivatives. Also, the terms “part,” “section,” “portion,” “member” or“element” when used in the singular can have the dual meaning of asingle part or a plurality of parts.

The term “detect” as used herein to describe an operation or functioncarried out by a component, a section, a device or the like includes acomponent, a section, a device or the like that does not requirephysical detection, but rather includes determining, measuring,modeling, predicting or computing or the like to carry out the operationor function.

The term “configured” as used herein to describe a component, section orpart of a device includes hardware and/or software that is constructedand/or programmed to carry out the desired function.

The terms of degree such as “substantially”, “about” and “approximately”as used herein mean a reasonable amount of deviation of the modifiedterm such that the end result is not significantly changed.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. For example, the size, shape, location ororientation of the various components can be changed as needed and/ordesired. Components that are shown directly connected or contacting eachother can have intermediate structures disposed between them. Thefunctions of one element can be performed by two, and vice versa. Thestructures and functions of one embodiment can be adopted in anotherembodiment. It is not necessary for all advantages to be present in aparticular embodiment at the same time. Every feature which is uniquefrom the prior art, alone or in combination with other features, alsoshould be considered a separate description of further inventions by theapplicant, including the structural and/or functional concepts embodiedby such feature(s). Thus, the foregoing descriptions of the embodimentsaccording to the present invention are provided for illustration only,and not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

What is claimed is:
 1. A centrifugal compressor adapted to be used in achiller system, the centrifugal compressor comprising: a casing havingan inlet portion and an outlet portion; an impeller attached to a shaftrotatable about a shaft rotation axis, the impeller having an impellershroud which encloses the impeller; a motor configured and arranged torotate the shaft in order to rotate the impeller; a diffuser disposed inthe outlet portion downstream of the impeller; and a seal bearingattached to the inlet portion to seal the impeller shroud, and rotatablysupporting the impeller and the shaft.
 2. The centrifugal compressoraccording to claim 1, wherein the seal bearing includes an oil supplygroove formed on a shroud facing surface of the seal bearing which facesthe impeller shroud.
 3. The centrifugal compressor according to claim 2,wherein the seal bearing further includes at least one oil return grooveformed on the shroud facing surface of the seal bearing.
 4. Thecentrifugal compressor according to claim 3, wherein the at least oneoil return groove includes a first oil return groove and a second oilreturn groove, and the oil supply groove is interposed between the firstoil return groove and the second oil return groove.
 5. The centrifugalcompressor according to claim 4, wherein the seal bearing furtherincludes a first separation groove and a second separation groove formedon the shroud facing surface of the seal bearing, the first oil returngroove is interposed between the oil supply groove and the firstseparation groove, and the second oil return groove is interposedbetween the oil supply groove and the second separation groove.
 6. Thecentrifugal compressor according to claim 5, wherein the first oilreturn groove and the first separation groove are disposed upstream of arefrigerant flow relative to the oil supply groove, and the second oilreturn groove and the second separation groove are disposed downstreamof the refrigerant flow relative to the oil supply groove.
 7. Thecentrifugal compressor according to claim 3, wherein the seal bearingfurther includes at least one separation groove formed on the shroudfacing surface of the seal bearing.
 8. The centrifugal compressoraccording to claim 7, wherein a first set of teeth and a second set ofteeth are formed on the shroud facing surface of the seal bearing, thefirst set of teeth being located between an end of the seal bearing andthe separation groove, and the second set of teeth being located betweenthe separation groove and the oil return groove.
 9. The centrifugalcompressor according to claim 8, wherein the at least one separationgroove receives oil and refrigerant which pass through the first set ofteeth and the second set of teeth, respectively.
 10. The centrifugalcompressor according to claim 7, wherein the separation groove has anannular shape extending circumferentially around the impeller shroud.11. The centrifugal compressor according to claim 7, further comprisingan oil sump configured and arranged to receive oil, oil being suppliedto the oil supply groove from the oil sump, and the oil being returnedto the oil sump via the oil return groove.
 12. The centrifugalcompressor according to claim 11, wherein oil containing refrigerant inthe separation groove is introduced into the oil sump in which oilcontaining refrigerant is separated into an oil portion and arefrigerant portion, and the refrigerant portion is returned to asuction side of the centrifugal compressor.
 13. The centrifugalcompressor according to claim 2, wherein the impeller shroud has astepped part which outwardly projects in a direction perpendicular tothe shaft rotation axis, the seal bearing has a recessed part whichreceives the stepped part, and the oil supply groove is provided in therecessed part.
 14. The centrifugal compressor according to claim 1,wherein the seal bearing is a radial bearing.